Multilayer spatial angular filter with airgap tuners to suppress grating lobes of 4x1 array antenna

A multilayer spatial angular filter with airgap tuners to suppress the grating lobes of a 4 x I array antenna is proposed. By using the airgap tuner, a commercial standard substrate can be chosen for the filter, to achieve its resonance condition, instead of lambda(g)/4 substrate. The measured beam patterns of the 4 x 1 array with the filter show that the grating and sidelobes are effectively diminished by 15 to 30 dB in the region of interest.